Bitcoin’s back, baby. The best-known and largest cryptocurrency has gained more than 130% in pandemic-ravaged 2020 and in November surpassed four separate $1,000-point barriers within a four-day span, going from $15,000 to $18,000. It’s a surge reminiscent of its wild ride in 2017-18, when it rose by 1,375% to within a whisker of $20,000 before falling by 70%. Some credit the rise to greater acceptance by Wall Street linchpins, including PayPal, which said in October it would allow customers to